Things were better when you were younger. Cars had some heft, you got smacked upside the head when you made a mistake and gosh darn-it, people knew how to speak properly! What is it with kids these days? Words that used to mean one thing, mean something totally different, and the words that do mean the same thing are pronounced bizarrely! The language of kids these days shows that something is wrong with our youth, with our education system, possibly with the whole world!
Well...not so much. If you feel this way about language you're probably suffering from something we linguists like to call The Golden Age Principle and almost everyone suffers from it at least now and then (even me). One of the beautiful and interesting things about human language is that it is constantly changing; sounds shift, pushing other sounds to shift, sounds merge together and split apart, words adopt new meanings, discard old ones, appear out of nothing and disappear into disuse.
To take an extreme example we need only look back to the source of the English language, We can't really go all the way to the beginning, there are no writings or recordings to help us figure out how language was structured when it first began to spit apart into separate families, but anthropologists, linguistics and biologists are studying what we do have and there are some things they're pretty confident about. English comes from a proto-language called Proto-Indo-European. We don't actually have any physical evidence to show how this language worked, but historical linguists use linguistic reconstruction to reverse engineer how it would have been structured. Indo-European branched off into a number of further language families as members dispersed geographically and lost contact with other groups. Over time the languages of each of these groups molded into something different. The Italic family branched off and became, among others, Latin, which spawned the Romance languages French, Spanish, Romanian etc. There was another branch as well: Germanic. As you may have guessed, German is a member of the Germanic language family, and so is English (also Dutch, Afrikaans, Frisian and Yiddish)!
You can see how time has changed the way we speak and the structure of language. Knowing that Armenian, Russian, Swedish, Afrikaans and English all come from the same root shows how much difference time and geography can make. And most of the time these changes don't come all at once because of some great moment in history, they come constantly and slowly, from one generation to the next. It's why no monolingual English speaker can understand German, but with a little help most can fully understand Shakespeare's English and with no help at all, their monolingual English neighbor.
To shrink down the time-frame a little more we can look at one of my favorite English, linguistic phenomena (mostly just because it has a cool name) ...THE GREAT VOWEL SHIFT!! The GVS is a huge change in pronunciation that began in the mid-1400s and levelled out by the mid-1700s. If you pronounce the sound /i:/, (it sounds like the vowel in “sleep”), you can feel that your tongue is high up and towards the front of your mouth. Compare this with /a/ (the vowel in “bad”), which puts your tongue low and back. Your tongue can be low, mid, or high and front, central or back to form vowels. The Great Vowel Shift occurred when vowel sounds that used to be pronounced low and central started to become more and more low and front. As a response to the closeness of this shifting sound, the preexisting low, front vowel started to be pronounced higher up, like a mid, front vowel to preserve a difference between the two. The vowel there then moved up again and so on and so on. When the highest front vowel was reached, it was pushed more centrally and the chain continued. Nearly every long vowel sound shifted at least one spot and in about three hundred years the pronunciation of nearly every word with a long vowel sound changed.
Now this might not be the fairest example. This was an incredibly massive change, more extensive than chain shifts usually are (hence the "Great"), but it does show how easily sounds can shift, and how fluid and natural the process is. This wasn't a planned or enforced change, it just happened and smaller vowel shifts of this nature have happened in other languages too.
So what does this have to do with the fact that your grandmother can't understand a word your kids are saying? Ask your parents if they think language has deteriorated since they were kids, then ask your grandparents, your great-grandparents. Most people will say yes, but this is not possible for at least two reasons. The first is, if language were deteriorating, our ability to communicate would be getting worse and worse and eventually we would reach a point where language as a system would fall apart completely. But if you look at the history you'll see that sounds shift and change, they bump into each other and sometimes combine, but they also sometimes split. If language were deteriorating we would be heading towards a point where there would be no difference between sounds, they would all slide together into one, and this isn't the case. Lexically, you might think that your kids vocabularies are smaller than yours was, but it's really just different. Did you have “Twitter”, “pwn” or “blog” in your vocabulary when you were their age? Words fall into disuse, it's true, and they should be mourned, but new words are constantly being born, words that express things that we didn't used to have a way to express, or describe things we simply didn't used to have.
Another problem with believing in a Golden Age is that this gives your parents the right to claim the same thing and then their parents too, and theirs and theirs. It should go all the way back to Proto-Indo-European, the true Golden Age of language, before those damn kids messed it up with their mumbling and their slang.
Language exists as a tool for communication, a way to let hunters tell other hunters where the good spots for deer are, where the threats hide, to create a stronger bond between partners, between mother and child, to help people teach other people how to stay alive, how to improve the world, to enable kids to complain about how antiquated their parents are, how they don't understand them at all. Language adapts as we adapt and shifts as we shift, it can wrap itself around new concepts effortlessly and forget old, useless ones without remorse. It's scary that we can see this change happen within our lifetimes and I readily admit that I can't claim never to fall prey to believing in a Golden Age. But when it happens, I try to step back, take a deep breath and trust in the future of language; so far it's done nothing but amazing things and that's something unbelievably exciting to look forward to, out of the mouths of babes.